Refractory coating methods considered preferable are those capable of fulfilling the following requirements:
(i) giving refractory coating layers as thin as possible which results in increasing of living space in the building; PA1 (ii) producing refractory coating layers as lightweight as possible which serve to mitigate the weight load to be supported by the lower floors of a high-rise building; PA1 (iii) forming stable refractory coating layers; PA1 (iv) giving refractory coatings which can exhibit good functions in the interface between the steel element and the coating, more specifically those which are unlikely to peel or flake in the interface therebetween, particularly when wetted or heated; PA1 (v) being easy to carry out and capable of easily applying the composition even to connections between the bases to be coated; PA1 (vi) giving coating layers which can exhibit the desired fire resistance within a short time after application; PA1 (vii) applying the composition without scattering the same about the surrounding, hence without staining the environment; PA1 (viii) using compositions which are easy to transport; PA1 (ix) forming coating layers which develop no crack; PA1 (x) requiring a small number of steps; PA1 (xi) comprising the steps which are easy to perform; PA1 (xii) being economical, etc.
The methods heretofore known for forming refractory coatings on steel elements include the PC method, spraying method, troweling method and concrete-placing method. The spraying method is subgrouped into dry or semi-wet spraying method and wet spraying method. These conventional coating methods have their own features but suffer drawbacks.
The molding plate method employs molding plates and has the following advantages and disadvantages. The advantages are as follows: (1) giving coatings which have constant quality because of use of molded or shaped plates manufactured in plants, not depending on the skills of operators, (2) enabling the completion of operation at a time even on bases which require 3 hours' fire resistance without involving repeated operations, (3) having the efficiency in work reduced to a lesser extent by the absence of one operator from a team usually of 3 or 4 operators than the spraying method, (4) effectively preventing the pollution from occuring due to the scatter of the composition about the environment by the wind, (5) achieving good efficiency in work because of the operation involving no scatter of composition in the environment. The disadvantages include (1) the need to study the layout and workability when setting molded plates to a complex place containing diverse kinds of steel elements and numerous connections as in elevator shafts and staircases which require cutting and adhering of shaped plates and like cumbersome labors, thereby reducing the efficiency in work, (2) the necessity of removing the adhesive forced out from between the shaped plate and the surface of the base when placing the shaped plates to nooks like return ducts as in elevator shafts and ceilings in order to prevent the adhesive forced out from being strewn in the environment, and (3) the need to use an adhesive in larger amounts to assure reliable adhesion, considering that the adhesive should not be applied in excess amount to the joint between the shaped plates when adhering shaped plates to steel elements and joining shaped plates to one another, in order to prevent undesirable shrinkage of the joint from occuring due to the vaporization of the sodium silicate during the hardening of the adhesive, the excess adhesive being unnecessary because of shaped plate units having relatively small size and involving low stress due to the heat distortion and narrow joints between shaped plates.
The PC method involves the use of precast concrete and has the advantages of saving the labor in construction site because of use of prefabricated blocks and panels and also being suitable for columns or pillars owing to the hard surface finish. On the other hand, the method possesses the drawbacks of involving the use of precast concrete elements which are cumbersome to handle in construction site because of the great weight; encountering difficulties in coping with the interlayer displacement of concrete blocks which would occur due to the high rigidity and hardness thereof, depending on the mode of application of blocks; and tending to form a layer of great thickness (low in fire resistance and heat insulation per unit thickness).
The spraying method is practiced by spraying coating compositions having an indeterminate form. The semi-wet spraying method uses a dry powdery composition with a low water content which is forced by air into the nozzle in the forward end of the spray to mix with water therein. The wet spraying method employs a liquid coating composition which is prepared by kneading with water and which is forced out by a pump. The former method is inexpensive and uses a spray device which is lightweight and easy to handle, but the method has the defects of (1) requiring thorough masking to prevent the scatter of the composition in spraying, (2) giving a layer which would peel if exposed to rain before being dried after application, (3) tending to form a layer irregular in quality without adequate quality control, (4) producing a layer susceptible to damage by ductwork or the like performed after application because of the soft layer formed and (5) involving the need to spray a finishing agent over the surface of the layer to prevent dust from evolving from the surface of the layer after hardening, depending on applied surfaces. The wet spraying method frequently uses a mixture of rock wool, cement and water and has the advantages of using coating compositions which can be pumped up to high-floor locations, leading to decrease in lifting costs and which is amenable to a base having a complicated shape. Nevertheless the method possesses the drawbacks of using coating compositions which involve difficulties in coping with the scatter of the composition in the environment and in controlling the quality, particularly the thickness of coating layer, and which require a considerable time in forming a coating with the desired hardness. The method further poses the problems of strewing the composition, consequently smearing the surrounding inside and outside the building; being carried out in poor working conditions; producing layers having low adherence to steel elements and poor corrosion resistance.
The troweling method is conducted by skillful plasterers using hand-trowels. The method can produce layers over bases of any shape and give jointless coating and pleasing finish, but provides coatings prone to develop cracks. Further the method involves an extremely low efficiency in work.
The concrete-placing method is performed by literally depositing concrete which is usally lightweight. The method has the advantages of using concrete having lightweight properties and high adherence to steel. The method suffers the shortcomings of giving coatings tending to develop cracks and thus essentially needing repair to restore the cracked portions, which presents complicated problems, such as difficulties in placing concrete into the cracks and in edge cutting, etc.
The conventional methods stated above have further drawbacks in respect of the materials used. The use of concrete materials results in layers which undergo marked contraction during hardening due to hydration of concrete, thereby involving low dimensional stability and the like. Rock wool and cement materials tend to produce coatings which are soft and which give off dust to a great degree. The method using molded plates requires additional use of adhesives which are cumbersome to handle. Plasters such as cement plaster, gypsum plaster, etc. need expanded metal lath bases. In addition, these compounds all require treatment of steel elements for corrosion prevention.
An object of this invention is to provide a method for forming refractory coatings free from the drawbacks of the foregoing conventional methods.
Another object of the invention is to provide a method for giving coatings having higher fire resistance than those formed by conventional methods.